Muscles Of The Shoulder Region.
Learning Objectives:
Shoulder Region
 It is the proximal part of upper limb.
 Surrounds the shoulder joint.
 Providing round counter at proximal end of upper extremity.
 Bony land marks are:
 spine of scapula,
 acrominon,
 Inferior angle of scapula.
Muscles Of Shoulder Region
Group of six muscles, converge from scapula on to the humerus and surround
the shoulder joint, Includes:
 Deltoid.
 Supraspinatus.
 Infraspinatus.
 Teres Minor.
 Teres major.
 Subscapularis.
Most of part of these muscles
are under the cover of Deltoid
and Trapezius.
Deltoid:
 A powerful muscle.
 Has longer leaner origin.
 Has three groups of muscle fibers
 Anterior,
 Middle &
 Posterior.
 Tip:
 Principle abductor of the arm.
 But it cannot initiate this action.
 Assisted by the supraspinatus muscles.
Greek- delta triangular shaped
 Origin: Lateral 1/3 of clavicle, acromion process, scapular spine.
 Insertion: deltoid tuberosity at shaft of humerus.
 Nerve Supply: Axillary Nerve (C5-C6).
Deltoid consists of three groups of muscle fibers:
 Anterior Fibers:
 arising from clavicle,
 fibers are parallel.
 Posterior Fibers:
 arising from spine of scapula,
 parallel fibers.
 Middle fibers:
 arising from the acromion, multipennate,
 most powerful muscle fibers,
 having seven septa inside mass, make the muscle multipennate.
Actions:
 Anterior fibers:
 flexes and medially rotates shoulder.
 Middle fibers:
 Abducts the shoulder.
 Posterior fibers:
extends and laterally rotates the shoulder.
 Tip: Anterior & Posterior fibers act like guy ropes to steady the arm
in abducted position .
 Common site for Intramuscular Injection (IM)
 On lateral side of bulge of shoulder.
 Axillary nerve is under the cover of deltoid,
 It winds around the posteriolateral aspect of shaft of humerus below the 5-6
cm of acromion.
 If IM injection is given using wrong technique may produce damage
to axillary nerve.
Supraspinatus
Latin- supra above spinatus spine
 Bipennate muscle.
 Provide great force pull to the muscle.
 Origin: Supraspinatus fossa of the scapula.
 Insertion: Greater tubercle of the humerus.
 Nerve Supply: Suprascapular nerve (C5-C6)
 Action:
 Initiate the abduction at shoulder joint for first 15 degree.
 Assists deltoid muscle in abducting arm at shoulder.
 Stabilizes the head of the humerus.
 Tip: The supraspinatus is the only muscle in the rotator cuff groups that
does not actually rotate the humerus
Infraspinatus
Latin- infra beneath spinatus spine
 Multipennate muscle.
 A bursa lies between the muscle and scapula,
 This bursa usually communicates with cavity of shoulder joint.
 Origin: Infrsapsinatus fossa of the scapula.
 Insertion: Greater tubercle of the humerus.
 Nerve Supply: Suprascapular nerve from the brachial plexus (C5-C6).
 Action: Lateral rotation of the shoulder, and stabilizes the head of the
humerus.
Teres Minor
Latin- teres round
 Origin: superior half of the lateral border.
 Insertion: Greater tubercle of the humerus.
 Nerve Supply: axillary nerve (C5 C6).
 Actions:
 Weak adductor of humerus,
 Laterally rotates the shoulder and
 Stabilizes the head of humerus on glenoid.
Tip:
It is synergist to Infraspinatus.
 Teres minor may sometimes fuse with infraspinatus.
Latin- teres round
 An offspring of subscapularis.
 It has migrated to the dorsal surface of Scapula.
 Origin: Inferior part of lateral border and inferior angle of the scapula.
 Insertion: medial lip intertubercular groove of the humerus.
 Nerve Supply: lower subscapular nerve (C5 C6).
 Action: It extends the shoulder, medially rotates the shoulder, Adducts the
shoulder.
 Tip: Its tendon can be transplanted posteriorly to provide lateral rotation.